Beating Darwin-Bragg losses in lab-based ultrafast X-ray experiments

The use of low temperature thermal detectors for avoiding Darwin-Bragg losses in lab-based ultrafast experiments has begun. An outline of the background of this new development is offered, showing the relevant history and initiative taken by this wor

Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy

Light-driven molecular reactions are dictated by the excited state potential energy landscape, depending critically on the location of conical intersections and intersystem crossing points between potential surfaces where non-adiabatic effects govern transition probabilities between distinct electronic states. While ultrafast studies have provided significant insight into electronic excited state reaction dynamics, experimental approaches for identifying and characterizing intersections and seams between electronic states remain highly system dependent. Here we show that for 3d transition metal systems simultaneously recorded X-ray diffuse scattering and X-ray emission spectroscopy at sub-70 femtosecond time-resolution provide a solid experimental foundation for determining the mechanistic details of excited state reactions. In modeling the mechanistic information retrieved from such experiments, it becomes possible to identify the dominant trajectory followed during the excited state cascade and to determine the relevant loci of intersections between states. We illustrate our approach by explicitly mapping parts of the potential energy landscape dictating the light driven low-to-high spin-state transition (spin crossover) of [Fe(2,2′-bipyridine)3]2+, where the strongly coupled nuclear and electronic dynamics have been a source of interest and controversy. We anticipate that simultaneous X-ray diffuse scattering and X-ray emission spectroscopy will provide a valuable approach for mapping the reactive trajectories of light-triggered molecular systems involving 3d transition metals

K - Pp bound system at J-PARC

The K̄NN bound system, symbolically denoted as "K-pp", is the simplest K̄-nuclear bound system which has been widely discussed as a consequence of the strongly attractive K̄N interaction in I = 0 channels. Many theoretical works have pointed out the existence of the "K-pp" bound system, but the calculated properties such as the binding energy and the width spread out due to the uncertainty of the K̄N interaction below the K̄+N mass threshold. Experimentally, there are several reports on observation of a "K-pp" candidate with the binding energy of around 100 MeV, however, no definitive evidence was available so far. At J-PARC, we conducted a experimental search for the "K-pp" bound system using K- + 3He reaction at 1.0 GeV/c where the "K-pp" is expected to be directly produced via the (K-, n) reaction. We finally observed a bound state below the K- +p+p mass threshold in the Λpn final state, which can be interpreted as the "K- pp" bound state. The possible existence of the "K- pp" state is discussed from both aspects of production and decay. © 2020 Author(s)

Observation of a K̄ NN bound state in the He 3 (K-, Λp)n reaction OBSERVATION of A K̄ NN BOUND STATE ... T. YAMAGA et al.

We have performed an exclusive measurement of the K-+He3→Λpn reaction at an incident kaon momentum of 1GeV/c. In the Λp invariant mass spectrum, a clear peak was observed below the mass threshold of K̄+N+N, as a signal of the kaonic nuclear bound state, K̄NN. The binding energy, decay width, and S-wave Gaussian reaction form factor of this state were observed to be BK=42±3(stat.)-4+3(syst.)MeV, ΓK=100±7(stat.)-9+19(syst.)MeV, and QK=383±11(stat.)-1+4(syst.)MeV/c, respectively. The total production cross section of K̄NN, determined by its Λp decay mode, was σKtotBRΛp=9.3±0.8(stat.)-1.0+1.4(syst.)μb. We estimated the branching ratio of the K̄NN state to the Λp and ς0p decay modes as BRΛp/BRς0p∼1.7, by assuming that the physical processes leading to the ςNN final states are analogous to those of Λpn. © 2020 American Physical Society

Liver-Expressed Antimicrobial Peptide 2 is a Hepatokine that Predicts Weight Loss and Complete Remission of Type 2 Diabetes Mellitus After Vertical Sleeve Gastrectomy in Japanese Individuals

Introduction: Vertical sleeve gastrectomy (VSG) is considered one of the most effective treatments for sustained weight loss and complete remission of type 2 diabetes mellitus (CR-T2DM). Liver-expressed antimicrobial peptide 2 (LEAP2), a ghrelin receptor antagonist peptide, is a metabolic hormone regulated by VSG. However, it is unknown whether LEAP2 can be used to predict the outcomes of VSG. This study aimed to evaluate LEAP2 as a predictive factor for weight loss and CR-T2DM after VSG. Methods: This retrospective study included 39 Japanese participants with obesity who underwent VSG. Serum LEAP2, des-acyl ghrelin (DAG), and other metabolic and anthropometric parameters were studied before and at 12 months after VSG. Receiver operating characteristics (ROC) curve was generated to evaluate predictive score for weight loss with cut-off value of > 50 percent excess weight loss (%EWL). ROC curve was also generated to assess CR-T2DM. Results: Serum LEAP2 levels were significantly higher in participants with body mass index (BMI) 32–50 kg/m2 than in those with normal weight. Participants with BMI > 50 kg/m2 had lower serum LEAP2 concentrations than those with BMI 32–50 kg/m2. VSG caused a significant reduction in serum DAG concentrations, but it did not affect serum LEAP2 concentrations in either male or female participants. Preoperative serum LEAP2 concentration of 2.88 pmol/mL was the optimal cutoff value for predicting weight loss after VSG, with sensitivity of 80.0% and specificity of 75.9%. Preoperative serum LEAP2 level higher than 4.67 pmol/mL predicted CR-T2DM after VSG with sensitivity of 100% and specificity of 58.8%, Discussion/Conclusion: Preoperative serum LEAP2 could predict weight loss and CR-T2DM as outcomes of VSG

The modern era of light kaonic atom experiments

This review covers the modern era of experimental kaonic atom studies, encompassing 20 years of activity, defined by breakthroughs in technological developments which allowed performing a series of long-awaited precision measurements. Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing the strange quark, which interacts in the lowest orbits with the nucleus also by the strong interaction. As a result, their study offers the unique opportunity to perform experiments equivalent to scattering at vanishing relative energy. This allows one to study the strong interaction between the antikaon and the nucleon or the nucleus "at threshold," namely, at zero relative energy, without the need of ad hoc extrapolation to zero energy, as in scattering experiments. The fast progress achieved in performing precision light kaonic atom experiments, which also solved long-pending inconsistencies with theoretical calculations generated by old measurements, relies on the development of novel cryogenic targets, x-ray detectors, and the availability of pure and intense charged kaon beams, which propelled an unprecedented progress in the field. Future experiments, based on new undergoing technological developments, will further boost the kaonic atom studies, thus fostering a deeper understanding of the low-energy strong interaction extended to the second family of quarks

Electronic structure and excited state properties of iron carbene photosensitizers - A combined X-ray absorption and quantum chemical investigation

The electronic structure and excited state properties of a series of iron carbene photosensitizers are elucidated through a combination of X-ray absorption measurements and density functional theory calculations. The X-ray absorption spectra are discussed with regard to the unusual bonding environment in these carbene complexes, highlighting the difference between ferrous and ferric carbene complexes. The valence electronic structure of the core excited FeIII-3d5 complex is predicted by calculating the properties of a CoIII-3d6 carbene complex using the Z+1 approximation. Insight is gained into the potential of sigma-donating ligands as strategy to tune properties for light harvesting applications